1. Field of the Invention
The present invention relates generally to the compression and encryption of data, and more particularly to compressing data with a human perceptual model.
2. Related Art
Computer applications, audio devices, and video devices based on digital data technology continue to appear in the marketplace. In response, the need for presenting audio and video signals in digital form continues to increase. In the video broadcasting area, conventional video broadcast systems include cable television systems and satellite-based broadcast systems. Although the scale and power of such systems continue to increase, the overall bandwidth available for transmitting video and audio signals remains limited. Thus, the need for signal compression remains central to digital communication and signal-storage technology. Competing with the need to compress data is the need to maintain the subjective visual quality of an image, arguably, the ultimate objective of video transmission systems. To this end, performance metrics that take the psycho visual properties of the human visual system (HVS) into account are needed. Visual sensitivity to: frequency, brightness, texture, and color are examples of psycho-visual properties. A few human visual models incorporating these psycho-visual properties into their algorithms include: just-noticeable-distortion (JND), visible difference predictor (VDP) and three-component image model. The JND model for example, provides each pixel with a threshold of error visibility, below which reconstruction errors are rendered imperceptible.
To balance these considerations, one problem to be solved for optimizing the delivery of digital data streams is how to locate perceptually important signals in each frequency subband. A second problem is how to encode these signals with the lowest possible bit rate without exceeding the error visibility threshold.
A third consideration in the video broadcasting industry is the need to maintain conditional access to the transmitted data. In a commercial setting, conditional access is used to control which customer can get particular program services. Specific programs are only accessible to customers who have satisfied prepayment requirements. Conditional access is often implemented by way of a key-based system involving a combination of scrambling and encryption to prevent unauthorized reception. Encryption is the process of masking the secret keys that enable the descrambler to unscramble transmitted signals into viewable scenes. The integrity of the various encryption routines used presently is constantly being tested. As a result, vulnerabilities are identified and the push to develop improved systems continues. In view of the considerations set forth above, what is presently needed is a secure system that effectively meets the need to provide high quality images while making efficient use of limited bandwidths.